When an angle modulated, e.g. FM, radio wave transmitted from a transmitting antenna reaches a receiving antenna via more than one different propagation path interference may occur between the received signals. The interference is apt to cause the received signal to include distortion components therein. In other words, the distortion (which is referred to as interference distortion hereinafter) of the received signal occurs since both a direct wave and an indirect wave, such as a reflected wave and/or a diffracted wave, are received by the same receiving antenna. The interference distortion which occurs due to the above mentioned reason is called a multipath distortion. The possibility of multipath distortion is relatively high in cities having tall buildings.
A method which has been adopted to reduce or cancel multipath distortion is to use a receiving antenna which has a sharp directivity for receiving only the direct wave or a wave which the antenna is aimed to receive. However, this method does not work effectively when many tall buildings surround a receiving point. Therefore, various types of compensation circuits for reducing the distortion have been provided hitherto. Although these conventional multipath distortion compensation circuits eliminate the distortion components to an extent, the distortion components included in the received signal cannot be removed perfectly since only approximate compensation is performed in these conventional circuits. Therefore, complete elimination of the multipath distortion components by use of these conventional compensation circuits does not necessarily occur.
Furthermore, the conventional compensation circuits properly function only when the magnitude of the direct wave received by a receiving antenna is greater than that of the indirect, i.e. reflected and/or diffracted, wave which is also received by the same antenna. When the magnitude of the indirect wave is greater than that of the direct wave, compensation of the distortion components is not adequately performed.